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positive and negative work



A conceptual question from the fifth edition of Serway and Faughn College physics (ch. 5 number 2):

"Discuss whether any work is being done by each of the following agents and, if so, whether the work is positive or negative:

d) the leg muscles of a person in the act of sitting down."

I say the muscles are doing negative work since they exert an upward force (to prevent the person from simply falling into the chair) while the motion of the person is down. The answer in the book is positive, with no explanation given.

Could someone explain this for me?

Justin Parke